1. Field of the Invention
The present invention relates to a slot antenna adapted to transmitting or receiving high-frequency signals of chiefly microwaves or millimeter waves.
2. Description of the Prior Art
In recent years, data have been transmitted in a wireless manner and on a personal basis as represented by portable telephones. Under such circumstances, it has been desired to transmit large amounts of data at higher speeds. For this purpose, semiconductor elements (high-frequency semiconductor elements) have been developed that operate in high-frequency regions such as of millimeter waves (30 to 300 GHz).
There have further been proposed various applied systems using high-frequency semiconductor elements that work on millimeter electromagnetic waves, as represented by a between-the-car radar and a wireless LAN. For example, in the Electronics Society, Japanese Academy of Electronic Data Communication, 1995, a between-the-car radar (see SC-7-6), a cordless camera system (see C-137), a high-speed wireless LAN (see C-139) and the like systems have been proposed.
These systems all utilize radio waves, and signals are exchanged through antennas between the system and space in which radio waves propagate. A variety kinds antennas have heretofore been studied for dealing with high-frequency signals as can be represented by a microstrip antenna, a horn antenna, a slot antenna and the like antennas.
The slot antenna has a structure in which a high-frequency signal transmission line such as a microstrip line is formed on one surface of a dielectric substrate, a ground layer is formed on the other surface thereof, a slot is formed in the ground layer at a position opposed to an open end of the transmission line, and the transmission line and the slot are electromagnetically coupled together. The slot antenna having such a structure is advantageous in that it can be easily produced by utilizing a general layer-laminating technology, it is particularly cheaply produced among the above-mentioned various kinds of antennas, and it is very suited for the systems that must be constructed in small sizes and in light weights.
However, the existing slot antennas have a defect of low efficiency (signal transmission characteristics) and, hence, it has been demanded to improve the efficiency.